I. Field of the Invention
This invention relates to a method and apparatus for the measurement of the quenchant properties of coolants, and in particular the use of such methods and apparatus for measurement of properties of coolants used in the direct chill (DC) casting of metals, particularly aluminum alloys. It also relates to the use of such a method and apparatus for control of coolants in casting processes.
II. Discussion of the Background Art
It is recognized that the quenching properties of coolants, particularly those used in cooling aluminum alloy slabs from high temperatures during casting, are very dependent on the coolant composition, including the presence of small amounts of contaminants. This is particularly important when such coolants are to be used above the "film boiling temperature," since the effectiveness of cooling can be rapidly altered by slight changes to the film boiling temperature itself.
Various techniques have been used to measure the quenchant properties of coolants in the past. For example, U.S. Pat. No. 5,178,463 (Berry et al) describes the use of a flame-heated plate on which the quenchant to be tested is sprayed, and the temperature gradient is used to determine quenchant properties.
U.S. Pat. No. 4,756,357 (Banniger et al) describes an electrically-heated plate within a casting mould where the flowing coolant passes the plate and the heat loss is measured. The signal is subsequently used for controlling the coolant flow or gas content.
Both these methods employ fairly large heated elements and require the use of substantial quantities of flowing coolant.
A paper entitled "The Effect of Cooling Water on Aluminum Ingot Casting" by H. Yu, describes a small cylindrical element containing a thermocouple which is preheated in a furnace then immersed in a sample of coolant. While this device is more compact than the devices required for the preceding methods, a separate preheating furnace is required, and the thermal response is limited because of the slow response time of the embedded thermocouple.
There is a need, therefore, for a compact and fast response system for measuring coolant quenchant properties, including properties above the film boiling temperature, that can also serve as part of a control system for altering the coolant flow or properties in response to changes in such quenchant properties.